The present invention relates to a semiconductor device and a manufacturing technique for the semiconductor device, and more particularly to a technology effectively applicable to a semiconductor device including HBTs (Heterojunction Bipolar Transistors) and a manufacturing technique for the semiconductor device.
For example, there are semiconductor elements using III-V compound semiconductor such as gallium arsenide (GaAs). The compound semiconductor is characterized in that it is higher in mobility than silicon (Si) and half-insulating crystals are obtained. In the compound semiconductor, mixed crystals can created, and heterojunctions can be formed.
One of semiconductor elements using heterojunction is heterojunction bipolar transistor (hereafter, referred to as “HBT”). The HBT is a bipolar transistor using gallium arsenide for its base layer, and indium gallium phosphate (InGaP), aluminum gallium arsenide (AlGaAs), or the like for its emitter layer. That is, the HBT is a bipolar transistor in which a heterojunction is formed using different semiconductor materials for the base layer and for the emitter layer.
The heterojunction makes it possible to make the forbidden band width of the emitter in a base-emitter junction larger than the forbidden band width of the base. Thus, it is possible to significantly increase carrier injection from emitter to base as compared with reverse charge carrier injection from base to emitter. Therefore, the HBT is characterized in that its current amplification factor is very large.
Since the HBT is very large in current amplification factor, as mentioned above, it is used in, for example, high-frequency amplifying systems (power amplifier modules) incorporated in cellular phones. In the power amplifier module, semiconductor chips in which HBTs are formed are mounted over a wiring substrate.
Patent Document 1 discloses a technology that implements the following: when a semiconductor chip with HBTs formed therein is mounted over a wiring substrate, pressure applied to the electrodes of the HBTs is reduced; further, lead-out electrodes and a package substrate (wiring substrate) are brought into contact with each other without fail for the enhancement of the reliability of the semiconductor device.
A more specific description will be given. An emitter lead-out electrode with which the emitter electrodes of a plurality of HBTs are connected in common is formed. In this emitter lead-out electrode, a dent is formed in the areas positioned above the individual emitter electrodes. Thus, during flip chip mounting during which the emitter lead-out electrode is brought into contact with the package substrate, the dents prevent bonding pressure from being applied to the emitter electrodes.
[Patent Document 1] Japanese Unexamined Patent Publication No. 2001-244274 (pp. 5 to 6, FIG. 5)